Your niece and your son are second cousins. Your niece's child and your son are second cousins once removed.
Well, it depends how close you are to your husbands family. If you really want to know they are cousins-in-law.
Your son and your aunt's child are first cousins, so your son and your aunts grandson (the son of your aunt's child) are first cousins, once removed.
Your son's child and your nephew are second cousins.
your son and your brother's son will be cousins
Your son and your 1st cousin's child are 2nd cousins.
Your daughter and your niece are first cousins. Your daughter than your niece's son are first cousin's once removed. Your daughter's child and your niece's child are second cousins to each other.
Your son and your sisters child are first cousins. The granddaughter is out of synch by a generation. That will make them first cousins once removed.
Your niece's child and your grandson's child (your great grandchild) are second cousins, once removed, to each other.
Your daughter and your niece are first cousins. Your daughter than your niece's son are first cousin's once removed. Your daughter's child and your niece's child are second cousins to each other.
Your nephew and your daughter are first cousins to each other. Your nephew's son and your daughter are first cousins, once removed. Your nephew's son and your daughter's child would be second cousins to each other.
First cousins once removed. Your child and your nephew are first cousins and there is one generation difference.